In The Odyssey, the Greeks believed that man is responsible for his fate. They believed in the sacredness in the guest-host relationship. Just as Odysseus and his men violated this relationship in the episode of the Cicones, and just as Polyphemus violated it in the episode in which he is blinded, so too do the suitors violate this relationship on Ithaca. They take advantage of custom to exploit the women, natural resources, and Telemachus' lack of manhood.
As such, the Greeks believed that recklessness and wrongdoing lead to punishment by the gods (or, in the case of the suitors, by Odysseus himself). Proper treatment of fellow humans: receiving of foreigners and guests (compare the correct behavior shown by Nestor (book 3, 34-74), Telemachos (book 1, 113-143) and the Phaecians (book 7, 167-181) with the improper behavior of the Cyclops (book 9, 250-306). Also the guests themselves have obligations. The suitors in Odysseus palace clearly misbehave and even insult other guests such as Odysseus, who is disguised as a beggar (book 17, 445-487).
The suitors insult both youth and old age in Telemachus and Odysseus (disguised as beggar). They insult women, Penelope and her maids, and they drain Ithaca of its natural resources (wine, food, sheep). They do not necessarily want her to choose a husband among them. In fact, they relish her indecision because it prolongs their stay and their festivity.
In the end, Odysseus punishes them in a bloody rampage because they overextend their stay and try to rob him of his position as king, father, and husband--the sacred trinity of manhood.